Benchmark of Density Functional Theory in the Prediction of 13C Chemical Shielding Anisotropies for Anisotropic Nuclear Magnetic Resonance-Based Structural Elucidation.

Abstract

Density functional theory (DFT) calculations have emerged as a powerful theoretical toolbox for interpreting and analyzing the experimental nuclear magnetic resonance (NMR) spectra of chemical compounds. While DFT has been extensively used and benchmarked for isotropic NMR observables, the evaluation of the full chemical shielding tensor, which is necessary for interpreting residual chemical shift anisotropy (RCSA), has received much less attention, despite its recent applications in the structural elucidation of organic molecules. In this study, we present a comprehensive benchmark of carbon shielding anisotropies based on coupled cluster reference tensors taken from the NS372 benchmark data set. Additionally, we investigate the representation of the DFT-predicted shielding tensors, such as the eigenvalues and eigenvectors. Moreover, we evaluated how various DFT methods influence the discrimination of possible relative configurations using recently published ΔΔRCSA data for a set of structurally diverse natural products. Our findings demonstrate that accurate interpretation of RCSAs for configurational and conformational analysis is possible with semilocal DFT methods, which also reduce computational demands compared to hybrid functionals such as the commonly used B3LYP.